The fact that OS X is currently in last place (I read the same article you're referring to - I think it was on OS News but I'm not sure) is the very reason why they can improve so drastically. Basically, what Apple meant to say is, they're going to be backporting all the FreeBSD scheduler patches to OS X - perhaps even using the ULE Scheduler which would be 1) easy enough to switch to without too much development on Apple's behalf and 2) totally capable of delivering the promised improvements.
http://neosmart.net/blog/2008/os-x-snow-leopard-to-use-ule-s...
Honestly, I don't understand why Apple continues to work on their own kernel. It has near zero competitive advantage relative to FreeBSD or Linux, and much cost a fortune to maintain. The real value of their product has always been above the kernel anyway: I have to believe that switching the kernel out for a more robust Unix variant can only be a good thing for the Mac.
As things stand right now, typical SMP scalability benchmarks put OS X solidly behind even Vista, and trailing Linux and FreeBSD by a mile (I wish I could find a cite for those -- they were doing the rounds a few months back, I think).